Reinforcing the knight's position and preventing any attempt by Black related to c5-c4.
12... d8c8  13. c3d5  13... a7a5  14. a2a4  14... g7g5 [%c_effect g5;square;g5;type;GreatFind;persistent;true] A typical Berlin move, gaining space on the kingside, which makes it difficult for White's pawns to advance. Furthermore, the knight cannot use the f4 square anymore.